Libraries (such as 'libtorch_cpu.so') and executables (such as 'torch_shm_manager')
get installed, quite surprisingly, to 'lib/python3.8/site-packages/{bin,lib}'.
Make sure RUNPATH matches that.

--- a/cmake/Dependencies.cmake
+++ b/cmake/Dependencies.cmake
@@ -4,7 +4,7 @@ if(APPLE)
   set(CMAKE_MACOSX_RPATH ON)
   set(_rpath_portable_origin "@loader_path")
 else()
-  set(_rpath_portable_origin $ORIGIN)
+  set(_rpath_portable_origin $ORIGIN/../lib)
 endif(APPLE)
 # Use separate rpaths during build and install phases
 set(CMAKE_SKIP_BUILD_RPATH  FALSE)

--- a/caffe2/CMakeLists.txt
+++ b/caffe2/CMakeLists.txt
@@ -1797,5 +1797,5 @@ if(BUILD_PYTHON)
   if(${BUILDING_WITH_TORCH_LIBS})
     # site-packages/caffe2/python/caffe2_pybind11_state
     # site-packages/torch/lib
-    set(caffe2_pybind11_rpath "${_rpath_portable_origin}/../../torch/lib")
+    set(caffe2_pybind11_rpath $ORIGIN/../../torch/lib)
   endif(${BUILDING_WITH_TORCH_LIBS})
